Field of Invention
The present invention relates generally to combined power and cooling generation systems, and, more particularly, to a combined power and refrigeration cascade system (“PARCS”) that includes an electric power system (PS) that produces both electric power and medium-to-high-grade waste heat that can be used for providing the cooling and power supply needs of data centers and the like.
Description of Prior Art
On-site power generation systems using combustion engines (for example, gas turbines) or fuel cells allow much higher energy efficiency through the utilization of the prime mover's waste heat. Such systems have been offered in a variety of configurations involving combined heat and power (“CHP”), combined cooling and power (“CCP”) or combined cooling, heat and power (“CCHP”). In all these configurations, the basic distinction is the mode of waste heat utilization, which is dictated by the type of load(s) served by the system. An important factor in determining the economic effectiveness of these systems is the matching of their power and thermal output to the time varying power and thermal demands of the load(s). Ideally, the power and thermal output (heating or cooing) of an on-site system should be fully utilized by the load at all times, which occurs very rarely except when the power and thermal (e.g., cooling) demands are strongly correlated, as they are in computer data centers.
CCP and CCHP systems typically use absorption chillers to utilize the waste heat for cooling. The most common type is single-effect or double effect LiBr—H2O absorption systems (ABS), modified to operate with the lower temperature waste heat from the power system. A CCP system comprising a 30%-efficient power generation system driving an R134a vapor compression (“VC”) water chiller (COPc˜6) and a double-effect absorption chiller (COPa˜1.1) can achieve a fuel-based cooling COP higher than 2.4 under typical water-cooled chiller operating conditions (5° C. evaporator/° 35 C condenser). It should be noted, however, that LiBr—H2O ABS use water as a refrigerant and cannot provide sub zero ° C. refrigeration, making such systems unsuitable for low-temperature refrigeration applications.
Systems comprising cascaded combinations of exhaust—driven ABS and VC cooling have been proposed in which the ABS acts as a heat rejection system for a bottoming VC system (see U.S. Pat. Nos. 4,745,768 and 4,869,069). While these systems offer the potential for providing efficient on-site low-temperature refrigeration, they still suffer from possible temporal mismatching when operated in grid-independent mode to serve time-dependent loads (for example, space heating and cooling or supermarket refrigeration).
Grid-independent operation offers several advantages, especially with DC power sources like fuel cells and DC loads like computers. With grid independence, in addition to avoiding the grid-connection costs and compliance with grid regulations, it is possible to eliminate several steps of power conversion from DC to AC or vice versa, which account for as much as a 50% power loss in data center applications.
Description Of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section, they are all hereby incorporated by reference into this document in their respective entirety(ies).